Diatonic substitution
A chord is replaced by another diatonic chord of the same function. For example, I can be replaced by iii or vi (all tonic). IV can be replaced by ii (both subdominant). Substitutes share common tones with the original.
- I → iii or vi (tonic group)
- IV → ii (subdominant group)
- V → vii° (dominant group)
Tritone substitution
A dominant seventh is replaced by another dominant seventh whose root is a tritone away. For example, G7 → Db7. Both share the same tritone (B and F), so the resolution to tonic still works.
Chromatic approach
A chord a half-step above or below the target is inserted before it. For example, before Cmaj7 you can place Dbmaj7 or Bmaj7. This creates smooth chromatic bass motion.
Practical tips
Start with diatonic substitutions — they are the gentlest. Tritone substitution is effective in jazz and funk. Chromatic approach works in any style. The main criterion: the substitution must preserve harmonic motion, not break it.